1. Field of the Invention
The invention relates to a method and apparatus for liquid treatment of wafer-shaped articles.
2. Description of Related Art
Liquid treatment includes both wet etching and wet cleaning, wherein the surface area of a wafer to be treated is wetted with a treatment liquid and a layer of the wafer is thereby removed or impurities are thereby carried off. A device for liquid treatment is described in U.S. Pat. No. 4,903,717. In this device the distribution of the liquid may be assisted by the rotational motion imparted to the wafer.
Techniques for drying a surface of a disc-shaped article are typically used in the semiconductor industry after cleaning a silicon wafer during production processes (e.g. pre-photo clean, post CMP-cleaning, and post plasma cleaning). However, such drying methods may be applied for other plate-like articles such as compact discs, photo masks, reticles, magnetic discs or flat panel displays. When used in semiconductor industry it may also be applied for glass substrates (e.g. in silicon-on-insulator processes), III-V substrates (e.g. GaAs) or any other substrate or carrier used for producing integrated circuits.
Various drying methods are known in the semiconductor industry, some of which utilize isopropyl alcohol to reduce surface tension of rinse water on a semiconductor wafer surface. See, e.g., U.S. Pat. No. 5,882,433. Improvements upon such methods, involving the use of heated isopropyl alcohol, are described in commonly-owned patent applications WO 2011/007287 and U.S. Ser. No. 12/914,802 (filed Oct. 28, 2010).
There remains a need, however, to develop improved methods for preventing pattern collapse in the submicroscopic structures formed on such semiconductor wafers, not only during such drying process but also during other liquid treatments. Pattern collapse can occur when the surface tension of a liquid moving radially outwardly across the surface of a rotating wafer applies a damaging or destructive force to the submicroscopic structures formed on the wafer surface.
The problem of pattern collapse becomes more serious as the diameter of semiconductor wafers increases. For example, the current generation of single wafer wet processing technology is designed for 300 mm diameter wafers, but the previous generation technology was designed for 200 mm wafers and a next generation may be designed for wafers of 450 mm or larger diameter.
In particular, as the wafer diameter increases, so too will the temperature differential between a liquid at the point where it is applied in a central region of the wafer and the same liquid after it has travelled radially outwardly to the periphery of the wafer.
The problem of pattern collapse also becomes more serious as the aspect ratio of the submicroscopic structures continues to increase. This is also an ongoing trend in the manufacture of semiconductor devices, as the pressure to reduce device dimensions in general applies more to the horizontal layout and less to the thickness direction.
Commonly-owned copending application Ser. No. 13/229,097, filed Sep. 9, 2011, describes a spin chuck with an infrared heater mounted stationarily between an upper surface of the rotating chuck and a lower surface of the rotating wafer held thereby. While this chuck provides improved wafer heating, a need has been identified to improve the consistency of the system performance from one wafer to the next.